Strain gages have been developed for measuring stresses in structures. Conventional strain gages include metallic foil type strain gages and semiconductor type strain gages. Metallic foil type strain gages typically include a wire having an electrical resistance which varies when subjected to stress. Semiconductor type strain gages typically include a piezoresistive material which varies in resistance when subjected to stress. Use of a conventional strain gage requires that the strain gage be fastened or adhered to the structure being measured for stresses.
Microelectromechanical systems or MEMS devices include micromachined substrates integrated with electronic microcircuits. Such devices may form, for example, microsensors or microactuators which operate based on, for example, electromagnetic, electrostrictive, thermoelectric, piezoelectric, or piezoresistive effects.
Conventional strain gages are often unsuitable for measuring stresses in a MEMS device. For example, conventional strain gages are often larger than the MEMS device itself. In addition, fastening or adhering a conventional strain gage to the MEMS device may actually increase the strength of the MEMS device, thereby reducing stress in the MEMS device and providing an inaccurate measurement of the actual stress in the MEMS device.
Accordingly, there is a need for the present invention.
A substrate for a MEMS device includes a base material having a first side, a poly silicon strain gage formed on the first side of the base material, a dielectric material disposed over the strain gage, and a conductive material in communication with the strain gage through the dielectric material, wherein the substrate is adapted to have at least one opening formed therethrough, and wherein the strain gage is adapted to be formed adjacent the at least one opening.